Abstract:

A process for introducing annular coated catalysts K into a reaction tube
of a tube bundle reactor, in which adhering pairs of annular coated
catalysts K formed in the preparation of the annular coated catalysts K,
before the introduction thereof into the reaction tube, are removed at
least partly from the annular coated catalysts K.

Claims:

1. A process for introducing a portion withdrawn from at least one
production charge of annular coated catalysts K into a reaction tube of a
tube bundle reactor for the purpose of charging this reaction tube with a
fixed catalyst bed suitable for performing a heterogeneously catalyzed
partial gas phase oxidation of an organic starting compound, which
comprises, before the withdrawal of the portion from the at least one
production charge and/or after the withdrawal but before the introduction
of the portion withdrawn into the reaction tube, removing adhering pairs
of annular coated catalysts K formed in the preparation of the at least
one production charge of annular coated catalysts K at least partly from
the at least one production charge and/or from the portion withdrawn.

2. The process according to claim 1, wherein the coated catalysts K
consist of an annular shaped support body and a coating of active
composition applied thereto, the external diameter of the annular shaped
support body being from 4 to 10 mm, its height from 2 to 10 mm and its
wall thickness from 1 to 4 mm.

3. The process according to claim 2, wherein the active composition
comprises at least one multielement oxide.

4. The process according to claim 3, wherein the multielement oxide is one
which comprisesa) the elements Mo, Fe and Bi, orb) the elements Mo and V,
orc) the element V and additionally P and/or Ti.

5. The process according to any of claims 1 to 4, wherein the adhering
pairs are removed by a process for screening with the aid of a screen.

6. The process according to claim 5, wherein, between the external
diameter E and the height H of the annular coated catalyst K, the
relationship H≦0.5E is satisfied and the screen has screen
orifices O1 within whose continuous outline a rectangle R with the
side lengths L and C can be inscribed with the proviso
M1,L>E≧2H>C>H,but not with the proviso
M1*,L>C≧2H.

7. The process according to claim 5, wherein, between the external
diameter E and the height H of the annular coated catalyst K, the
relationship E≧H>0.5E is satisfied and the screen has screen
orifices O3 within whose continuous outline a rectangle R with the
side lengths L and C can be inscribed with the proviso
M3,L>E<2H>C>H,but not with the proviso
M3*,L≧C≧2H.

8. The process according to claim 6, wherein the screen orifice O1 is
a rectangle with the side lengths L and C.

9. The process according to claim 7, wherein the screen orifice O3 is
a rectangle with the side lengths L and C.

10. The process according to claim 6, wherein the screen orifice O1
is an elongated hole which derives from a rectangle with the side lengths
L and C.

11. The process according to claim 7, wherein the screen orifice O3
is an elongated hole which derives from a rectangle with the side lengths
L and C.

12. The process according to any of claims 1 to 11, which is followed by a
process for heterogeneously catalyzed partial gas phase oxidation of an
organic starting compound in the reaction tube charged with the fixed
catalyst bed.

13. The process according to claim 12, wherein the heterogeneously
catalyzed partial gas phase oxidation is the gas phase oxidation of
acrolein to acrylic acid or the gas phase oxidation of o-xylene and/or
naphthalene to phthalic anhydride.

14. A process for preparing annular coated catalysts by applying a
catalytic active composition to annular shaped support bodies with the
aid of a liquid binder, which comprises, after the preparation process
has ended, at least partly removing adhering pairs of coated catalyst
rings formed in the preparation.

15. The use of annular coated catalysts which have been prepared by a
preparation process according to claim 14 for charging reaction tubes in
a tube bundle reactor with a fixed catalyst bed.

16. A packing obtained by enveloping a portion of shaped catalyst bodies
with a packing medium, wherein the shaped catalyst bodies comprise
annular coated catalysts which have been prepared by a process according
to claim 14.

Description:

BACKGROUND OF THE INVENTION

[0001]The present invention relates to a process for introducing a portion
withdrawn from at least one production charge of annular coated catalysts
K into a reaction tube of a tube bundle reactor for the purpose of
charging this reaction tube with a fixed catalyst bed suitable for
performing a heterogeneously catalyzed partial gas phase oxidation of an
organic starting compound.

[0002]Processes for heterogeneously catalyzed partial gas phase oxidation
of organic starting compounds in fixed catalyst beds disposed in the
reaction tubes of tube bundle reactors are known for the preparation of
numerous industrial chemicals.

[0004]While a full oxidation of an organic compound with molecular oxygen
is understood in this document to mean that the organic compound is
converted under the reactive action of molecular oxygen such that all of
the carbon present in the organic compound is converted to oxides of
carbon and all of the hydrogen present in the organic compounds to oxides
of hydrogen, all different exothermic conversions of an organic compound
under the reactive action of molecular oxygen are summarized in this
document as partial oxidations of an organic compound.

[0005]In particular, in this document, partial oxidations shall be
understood to mean those exothermic conversions of organic compounds
under the reactive action of molecular oxygen in which the organic
compound to be oxidized partially, after the conversion has ended,
comprises at least one oxygen atom more in chemically bound form than
before the partial oxidation was performed.

[0006]A tube bundle reactor is normally an apparatus which comprises a
vertically arranged bundle of reaction tubes which is surrounded by a
reactor jacket, both ends of the individual reaction tubes being open and
the upper end of each reaction tube ending sealed into a passage orifice
of an upper tube plate sealed at the top into the reactor jacket and the
lower end ending sealed into a passage orifice of a lower tube plate
sealed at the bottom into the reactor jacket, the exterior of the
reaction tubes, the upper and the lower tube plate and the reactor jacket
together delimiting the reaction tube surrounding space, and each of the
two tube plates being spanned by a reactor hood having at least one
orifice. In the performance of a heterogeneously catalyzed partial gas
phase oxidation in such a tube bundle reactor, its reaction tubes are
charged with a fixed catalyst bed (a fixed catalyst bed is introduced
into its reaction tubes; a fixed catalyst bed is disposed in its reaction
tubes) and a reaction gas input mixture which comprises the organic
compound (organic starting compound) to be oxidized partially and
molecular oxygen is fed in through the at least one orifice in one of the
two reactor hoods, and the product gas mixture which comprises the target
product which results through partial gas phase oxidation of the organic
starting compound to be oxidized partially to the desired target product
as it flows through the fixed catalyst bed disposed in the reaction tubes
is removed via the at least one orifice of the other reactor hood, while
at least one (generally liquid) heat exchange medium is conducted around
the reaction tubes on the jacket side of the tube bundle reactor.
Normally, in the case of use of at least one liquid heat exchange medium,
it is conducted around the reaction tubes such that each of the two
surfaces of the two tube plates facing one another is wetted by liquid
heat exchange medium. The at least one (for example liquid) heat exchange
medium is typically conducted into the reaction tube surrounding space
with a temperature THin and back out of the reaction tube
surrounding space with the temperature of THout.

[0007]The statement that the reaction tubes are sealed into the passage
orifices in the upper and lower tube plate means that there is no means
of passage for the heat exchange medium between the reaction tube outer
wall and the bore wall (i.e. wall of the passage orifice or else shell of
the passage orifice). Such a seal can be effected, for example, as
described in DE-20 2006 014 116 U1.

[0009]In general, the components of the tube bundle reactor are
manufactured from steel. Useful manufacturing steel is both stainless
steel (for example of DIN materials number 1.4541 or 1.4571) and black
steel or ferritic steel (for example DIN materials 1.0481, 1.0315 or
material 1.0425). Frequently, all components of the tube bundle reactor
are manufactured from the same steel type. In many cases, the reactor
hoods are manufactured from ferritic steel and plated on their inner side
with stainless steel. In some cases, the reactor jacket is also
manufactured from a different steel type from the remaining part of the
tube bundle reactor, since rolled steel can be used for its production.

[0010]In this document, the reaction tube surrounding space is defined as
the space delimited by the exterior of the reaction tubes, the two tube
plates and the reactor jackets together, within which the at least one
(generally liquid) heat exchange medium is conducted. In the simplest
manner, in the reaction tube surrounding space, only one (preferably
liquid) heat exchange medium is conducted (such a procedure is also
referred to as a one-zone method in the one-zone tube bundle reactor). It
is typically fed to the reaction tube surrounding space at its upper or
at its lower end with its entrance temperature THin through
orifices in the reactor jacket, and conducted back out of the reaction
tube surrounding space at the opposite end with an exit temperature of
THout through orifices in the reactor jacket.

[0011]As a result of the exothermicity of the gas phase partial
oxidations, during the performance of a heterogeneously catalyzed partial
gas phase oxidation, THout≧THin (equality
relates to the case of evaporative cooling). With the aid of a heat
exchanger, heat is typically withdrawn from a portion or the entirety of
the (preferably liquid) heat exchange medium conducted out of the
reaction tube surrounding space before it is fed back to the reaction
tube surrounding space with the temperature THin.

[0012]In the reaction tube surrounding space, the (preferably liquid) heat
exchange medium can in principle be conducted around the reaction tubes
in simple co- or countercurrent to the reaction gas mixture flowing
within the reaction tubes. However, it can also be conducted around the
reaction tubes in a meandering manner with the aid of corresponding
deflecting plates, such that only over the entire reaction tube
surrounding space does a cocurrent or countercurrent to the flow
direction of the reaction gas mixture in the reaction tubes exist. When
the heat exchange medium used is liquid under the use conditions, it
should, appropriately from an application point of view, have a melting
point in the range from 0 (or from 50) to 250° C., preferably from
120 to 200° C.

[0013]Useful such liquid heat exchange media include, for example, melts
of salts such as potassium nitrate, potassium nitrite, sodium nitrite
and/or sodium nitrate, and also melts of metals such as potassium,
sodium, mercury and alloys of different metals. However, it is also
possible to use ionic liquids (in which at least one of the oppositely
charged ions comprises at least one carbon atom) or heat carrier oils
(e.g. high-boiling organic solvents such as mixtures of Diphyl® and
dimethyl phthalate). Useful gaseous heat exchange media include, for
example, steam under elevated pressure or else flue gases. Evaporative
cooling can, for example, also be undertaken with boiling water under
pressure.

[0014]To improve the selectivity of target product formation, the
heterogeneously catalyzed partial gas phase oxidation of an organic
compound can also be performed as a multizone method (for example
two-zone method) in a multizone tube bundle reactor (for example in a
two-zone tube bundle reactor). In this case, within the reaction tube
surrounding space, (for example two), essentially spatially separate
(preferably liquid) heat exchange media (which are normally of the same
type) are conducted (these may, for example, be separated by separating
tube plates which have corresponding passage orifices for the reaction
tubes and are inserted into the reaction tube surrounding space).

[0016]Within the particular temperature zone, the (preferably liquid) heat
exchange medium can be conducted as in the one-zone method (also relative
to the flow direction of the reaction gas mixture). For the difference
between THout and THin, the statements regarding the
one-zone method apply in an essentially identical manner to the
individual temperature zone.

[0017]A graphic distinction between a one-zone method and a two-zone
method (between a one-zone tube bundle reactor and a two-zone tube bundle
reactor) is shown schematically, for example, by the figures of DE
102007019597.6 and the figures of EP-A 1695954. Aside from these,
multizone methods are described, for example, in documents EP-A 1734030,
DE-A 10313214, DE-A 10313219, DE-A 10313211, DE-A 10313208 and in the
prior art cited in these documents. They are advantageous in particular
when a high loading of the fixed catalyst bed with the organic compound
to be oxidized partially is selected. The loading of the fixed catalyst
bed with reaction gas mixture or with one reaction gas mixture component
is understood to mean the amount of reaction gas mixture or reaction gas
mixture component in standard liters (I (STP); the volume that the
corresponding amount would theoretically take up in gaseous form at
0° C. and 1 atm) which is conducted through one liter of fixed
catalyst bed per hour (pure inert beds are not included).

[0018]The temperature THin of the at least one (preferably
liquid) heat exchange medium in heterogeneously catalyzed partial gas
phase oxidations of organic starting compounds is typically in the range
from 200 to 500° C., frequently in the range from 250 to
400° C. and in many cases in the range from 250 to 310° C.

[0019]The working pressure in a heterogeneously catalyzed partial gas
phase oxidation may be either below standard pressure (for example up to
0.5 bar; the reaction gas mixture is sucked through) or above standard
pressure. Typically, the aforementioned working pressure will be at
values of from 1 to 5 bar, frequently from 1.5 to 3.5 bar (in each case
absolute). Normally, the working pressure in a heterogeneously catalyzed
partial gas phase oxidation of an organic starting compound will not
exceed 100 bar.

[0020]The reaction gas input mixture (or else reaction gas entry mixture)
itself may, in the different procedures in the tube bundle reactor, be
conducted either from the top downward or from the bottom upward in the
reaction tubes (i.e. the at least one feed orifice may be disposed either
in the upper reactor hood or in the lower reactor hood). The same applies
to the conduction of the (preferably liquid) heat exchange medium.

[0021]The reaction gas input mixture may, on entry into the reaction
tubes, in principle be preheated to the temperature of the heat exchange
medium flowing on the corresponding tube plate underside.

[0022]The temperature of the reaction gas entry mixture, on entry into the
reaction tubes, may, though, also be below this temperature of the heat
exchange medium. This is advisable when the reaction tubes, in flow
direction of the reaction gas mixture, are charged first with a
longitudinal section of shaped bodies inert to the partial oxidation,
before the catalytically active section of the fixed catalyst bed
comprising shaped bodies having catalytically active composition begins.
In the course of flow through this inert section, the reaction gas entry
mixture may then be heated to the temperature of the heat exchange medium
which flows around the corresponding catalytically active reaction tube
section. In principle, the reaction gas entry mixture (the product gas
mixture) can also be fed in (removed) via more than one feed orifice
(removal orifice) present in the corresponding reactor hood. In general,
though, both the feed of the reaction gas entry mixture and the removal
of the product gas mixture are each effected via only one orifice in the
corresponding reactor hood.

[0023]Frequently, a heterogeneously catalyzed partial gas phase oxidation
of an organic compound can, in spatial terms, be connected immediately
downstream of a heterogeneously catalyzed partial gas phase oxidation of
another organic compound (in this case, the target product of the
preceding partial oxidation is normally the organic compounds to be
oxidized partially in the downstream partial oxidation) or connected
upstream of it. In particular, in these cases, the feeding or removing
reactor hood can be reduced to a cylindrical tube orifice (designed as a
cylindrical tube opening), which may, for example, form a cylindrical
transition to an aftercooler (cf., for example, DE-A 10 2004 018267 and
DE 102007019597.6).

[0024]It will be appreciated that it is also possible to perform two
heterogeneously catalyzed partial gas phase oxidations which are two
successive gas phase partial oxidation steps in immediate succession in
the reaction tubes of a multizone tube bundle reactor (for example in a
two-zone tube bundle reactor), in which case the charge of the fixed
catalyst bed in the reaction tubes of the multizone tube bundle reactor
normally changes in a corresponding manner at the transition from one
reaction step to the next reaction step (cf., for example, the
performance of multistage heterogeneously catalyzed partial gas phase
oxidations in the so-called "single reactor" according to EP-A 1388533,
U.S. Pat. No. 6,069,271, EP-A 990636, US-A 2006/0161019 and EP-A
1106598). Examples of the performance of such multistage heterogeneously
catalyzed partial gas phase oxidations in the multizone tube bundle
reactor (for example two-zone tube bundle reactor) are the
heterogeneously catalyzed partial gas phase oxidation of propylene to
acrylic acid and of isobutene to methacrylic acid.

[0025]In addition to molecular oxygen and the organic starting compounds
to be oxidized partially as reactants, the reaction gas input mixture of
a heterogeneously catalyzed partial gas phase oxidation generally also
comprises a diluent gas which behaves essentially inertly under the
conditions of the heterogeneously catalyzed gas phase partial oxidation.
In this document, this is understood to mean those diluent gases whose
constituents, present in the reaction gas mixture, under the conditions
of the heterogeneously catalyzed partial gas phase oxidation--each
constituent taken alone--remain unchanged to an extent of more than 95
mol %, preferably to an extent of more than 99 mol %. They have the task
firstly of absorbing some of the heat of reaction and conducting it out
of the tube bundle reactor as a constituent of the product gas mixture,
and secondly of ensuring that the reaction gas mixture is generally
outside the explosion range. Inert diluent gases typically suitable for
heterogeneously catalyzed partial gas phase oxidations of organic
starting compounds are, for example, N2, CO2, steam, noble
gases and in many cases also saturated hydrocarbons (for example in a
partial oxidation of unsaturated organic compounds) or mixtures of all or
of some of the aforementioned possible inert diluent gases.

[0026]The reactants present in the reaction gas mixture of a
heterogeneously catalyzed partial gas phase oxidation (O2 and the
organic starting compound) are converted as the reaction gas mixture
passes through the fixed catalyst bed disposed in the reaction tubes
during the residence time of the reactants over the catalyst surface.

[0027]The reaction tubes in the tube bundle reactor are, as already
mentioned, generally manufactured from ferritic steel or from stainless
steel and frequently have a wall thickness of a few mm, for example from
1 to 3 mm. Their internal diameter is usually a few cm, for example from
10 to 50 mm, frequently from 15 to 30 mm, or from 20 to 30 mm. The tube
length extends normally to a few meters (a typical reaction tube length
is in the range from 1 to 10 m, frequently from 2 to 8 m or from 2 to 6
m, in many cases from 2 to 4 m).

[0028]Appropriately from an application point of view, the number of
reaction tubes accommodated in the tube bundle reactor is at least 1000,
frequently at least 3000 or 5000 and in many cases at least 10 000.
Frequently, the number of reaction tubes accommodated in the tube bundle
reactor is from 15 000 to 30 000, or to 40 000, or to 50 000. Tube bundle
reactors having a number of reaction tubes above 50 000 are usually the
exception. Within the reaction tube surrounding space, the reaction tubes
are normally arranged in essentially homogeneous distribution, the
distribution appropriately being selected such that the distance of the
central internal axes of mutually adjacent reaction tubes (the so-called
reaction tube pitch) is from 25 to 55 mm, frequently from 35 to 55 mm.

[0029]Especially in the case of tube bundle reactors with a relatively
large cross section of their tube plates, it is appropriate from an
application point of view to leave a region without tubes in the center
of the tube bundle reactor, and instead to support the upper tube plate
within this region.

[0030]In principle, the total number of reaction tubes is distinguished
into working tubes (the overwhelming majority of the reaction tubes) and
into thermal tubes. While the working tubes are those reaction tubes in
which the heterogeneously catalyzed partial gas phase oxidation in the
actual sense is performed, thermal tubes primarily serve the purpose of
monitoring and controlling the reaction temperature as a representative
of the other reaction tubes (the working tubes). For this purpose, the
thermal tubes, in addition to the fixed catalyst bed, normally comprise a
thermowell which is conducted along the center of the thermal tube and is
charged merely with a temperature sensor (for example a
multithermoelement or an axially movable single thermoelement) (this is
in many cases, but not necessarily, compensated for by an elevated
internal diameter of the thermal tubes compared to the working tubes). In
general, the number of thermal tubes in a tube bundle reactor is very
much smaller than the number of working tubes. Normally, the number of
thermal tubes is ≦20. In this context, it is of particular
significance that the thermal tubes are charged with fixed catalyst bed
such that the profile of the reaction temperature along the interior of a
thermal tube corresponds very accurately to the profile of the reaction
temperature along the interior of a working tube (cf. EP-A 873 783 and
EP-A 1270 065).

[0031]The profile of the reaction temperature in the reaction tubes is
determined firstly by the evolution of heat caused by the exothermicity
of a heterogeneously catalyzed partial gas phase oxidation and secondly,
inter alia, by the transfer of this heat of reaction to the at least one
heat exchange medium conducted within the reaction tube surrounding
space.

[0032]Since heterogeneously catalyzed partial gas phase oxidations are
typically markedly exothermic reactions, and the heat of reaction is
transferred to the at least one heat exchange medium at a finite rate,
the temperature of the reaction gas mixture in the course of reactive
passage thereof through the fixed catalyst bed is normally different from
the temperature of the fluid heat exchange medium which flows around the
fixed catalyst bed outside the reaction tubes. It is typically above the
entrance temperature of the heat exchange medium THin into the
corresponding reaction zone (temperature zone) and, along a reaction
zone, generally passes through an absolute maximum (hotspot maximum) or
falls proceeding from an absolute maximum value (if appropriate via
further relative maxima). These maximum values of the reaction
temperature (of the temperature of the reaction gas mixture) are
typically referred to as so-called "hotspot temperatures".

[0033]The hotspot temperature is therefore of particular significance
because, where the reaction temperature in the reaction tube is elevated
(the temperature of the fixed catalyst bed corresponds essentially to the
temperature of the reaction gas mixture at the particular point), the
irreversible aging processes in the fixed catalyst bed also proceed at an
increased rate and cause accelerated deactivation of the fixed catalyst
bed.

[0034]In this regard, it is known from the prior art that heterogeneously
catalyzed partial gas phase oxidations in the reaction tubes of a tube
bundle reactor which have been charged with a fixed catalyst bed can be
performed over comparatively long periods (up to several years) in the
case of careful operation without the fixed catalyst bed in the reaction
tubes having to be renewed (freshly charged) (cf., for example, DE-A 10
350 822, DE-A 10 2004 025 445, EP-A 17 34 030 and the prior art
acknowledged in these documents). The irreversible deactivation of the
fixed catalyst bed is counteracted under otherwise essentially unchanged
operating conditions typically by an increase in THin and/or an
increase in the working pressure in the reaction tubes (cf., for example,
EP-A 11 06 598, DE-A 10 351 269, EP-A 17 34 030, EP-A 990 636, DE-A 10
2004 025 445). These measures allow the target product space-time yield
to be retained over prolonged operating times. However, they cause the
aging process of the fixed catalyst bed to be accelerated further to an
increasing extent (particular aging processes within the catalysts which
contribute to aging proceed, for example, more rapidly). On attainment of
a maximum value of THin, the fixed catalyst bed finally has to
be exchanged completely (cf. also DE-A 10 232 748, EP-A 11 06 598 and
DE-A 10 2007 010 422).

[0035]However, a disadvantage of such a complete exchange is that it is
comparatively complicated. The process for target product preparation has
to be interrupted for a prolonged period and the costs of catalyst
preparation are likewise considerable.

[0036]What are likewise desired are therefore procedures which are helpful
in as far as possible prolonging the lifetime of the fixed catalyst bed
in the tube bundle reactor.

[0037]As already mentioned, the above is possible to a certain extent in
the case of careful operation. Careful operation is understood in the
prior art to mean operating the tube bundle reactor, within the context
of what is possible, overall, such that, within the individual reaction
tubes, as far as possible, a uniform reaction behavior and hence also a
very uniform profile of the reaction temperature (of the temperature of
the reaction mixture and of the temperature of the fixed catalyst bed) is
present along the individual reaction tubes.

[0039]According to the teaching of JP-A 2006-142288, the reaction tube
inner surface should additionally have a very low surface roughness in
order to ensure very uniform charging of the reaction tubes with fixed
catalyst bed.

[0040]Such a very uniform charging of the reaction tubes with the same
fixed catalyst bed is also recommended by the documents U.S. Pat. No.
4,701,101, EP-A 14 66 883, WO 03/057653, US-A 2006/245992, US-A
2002/136678, WO 2005/051532, WO 03/076373 and JP-A 2004/195279.

[0041]At the same time, it is quite generally attempted in heterogeneously
catalyzed gas phase reactions to minimize the energy demand required for
the conveying of the reaction gas. As a measure for achieving this
objective, preference is given to using annular shaped catalyst bodies
for the configuration of the fixed catalyst bed, since they cause a
particularly low pressure drop in the course of passage of the reaction
gas through the fixed catalyst bed (cf., for example, WO 2005/03039). A
further advantage of annular shaped catalyst bodies normally consists in
reduced diffusion pathways and, resulting from this in many cases, in an
improved target product yield.

[0042]In the simplest case, such an annular shaped catalyst body consists
only of catalytically active composition which may, if appropriate, be
diluted with inert material (which is, for example, in many cases
incorporated for reinforcement reasons) (if appropriate, shaping
assistant is also present; for example graphite). Such annular geometric
shaped catalyst bodies are typically referred to as annular unsupported
catalysts.

[0043]However, a disadvantage of annular unsupported catalysts is their
generally not fully satisfactory mechanical stability in the course of
filling into the reaction tubes. Although this can be improved by an
increase in their wall thickness, a disadvantage of relatively large wall
thicknesses is that they are accompanied by a lengthening of the
diffusion pathway out of the reaction zone, which promotes undesired
subsequent reactions and hence reduces the target product selectivity.

[0044]A resolution of the contradiction which exists in the case of
unsupported catalyst rings between required mechanical stability
(increasing wall strength) on the one hand and limiting of the diffusion
pathway out of the reaction zone (decreasing wall strength) on the other
hand, while maintaining the otherwise particularly advantageous ring
geometry, is opened up by annular coated catalysts. These are annular
shaped catalyst bodies which consist of an annular (mechanically
particularly stable) (catalytically inactive) shaped support body which
is generally inert with regard to the gas phase partial oxidation and a
catalytically active composition (active composition) applied to its
surface.

[0045]It can be prepared, for example, by coating the annular shaped
support bodies (generally consisting of catalytically inactive
(frequently oxidic (e.g. hard-fired)) material; consisting of inert
material) with finely divided active composition using a generally liquid
binder. Alternatively (or in a mixture with finely divided precursor
composition), the shaped support bodies may also be coated with a finely
divided precursor composition of the active composition using a generally
liquid binder, and the conversion to the active annular shaped catalyst
bodies can be effected by subsequent (for example oxidative and/or
reductive) thermal treatment (if appropriate in an atmosphere comprising
molecular oxygen). The coating can be effected in the simplest manner,
for example, by moistening the surface of an inert annular shaped support
body (or else simply just "support body") by means of a liquid binder and
then adhering finely divided (pulverulent) active composition or finely
divided (pulverulent) precursor composition on the moistened surface.
Subsequently, normally at least a portion of the liquid binder (generally
under the action of heat) is volatilized before the annular coated
catalysts are ready to charge a reaction tube (a further thermal
treatment can be effected, for example, within the reaction tubes (for
example for the purpose of removing residual binder [cf., for example,
DE-A 102005010645])). Alternatively, the annular shaped support bodies
can also be sprayed with a suspension of finely divided active
composition and/or finely divided precursor composition.

[0046]Instead of coating the generally inert annular shaped support body
with finely divided active composition or with finely divided precursor
composition, the annular shaped support body can in many cases also be
impregnated with a solution (a molecular and/or colloidal solution) of
the catalytically active substance or with a solution of a precursor
substance and then the solvent can be volatilized and, if appropriate, a
chemical reduction and/or thermal treatment (if appropriate in a
molecular oxygen-comprising atmosphere) can follow. The annular shaped
catalyst bodies which result in this way are frequently also referred to
as supported or impregnated catalysts in the literature. However, they
will likewise be encompassed in this document under the generic term
"coated catalysts".

[0048]An unwanted by-product, which, though, generally cannot be avoided
completely, in the preparation of annular coated catalysts is the
formation of adhering pairs of annular coated catalysts. These are two
coated catalyst rings which adhere firmly to one another. Their formation
is attributable ultimately to the fact that the normally liquid binder
typically used to apply the active composition coating to the annular
support body in the preparation of coated catalysts is capable of
bringing about not only the bonding of active composition and shaped
support body but, to a limited degree, also the unwanted bonding of two
annular coated catalysts. Essentially, the formation of such adhering
pairs is restricted to two types: a) fused adhering pairs and b) tandem
adhering pairs.

[0049]In the fused adhering pairs, two annular coated catalysts (an
annular coated catalyst has the geometry E×I×H (external
diameter×internal diameter×height)) adhere to one another by
their cylindrical shells (outer walls) essentially over the entire height
H. They essentially adhere to one another resting alongside one another
at the same height (their outer surfaces adhere to one another).

[0050]In the tandem adhering pairs, two annular coated catalysts adhere to
one another by their annular cross-sectional areas which delimit the
particular coated catalyst ring at the top and at the bottom. The upper
ring surface of one coated catalyst ring adheres on the lower ring
surface of one coated catalyst ring adheres (sticks) on the lower ring
surface of the other coated catalyst ring. In this way, what is
effectively formed is a coated catalyst super-ring which has the same
external diameter E and the same internal diameter I as the two coated
catalyst rings which constitute it, but whose height is 2 H.

[0051]While the formation of tandem adhering pairs in the preparation of
annular coated catalysts is essentially unavoidable, fused adhering pairs
form in the preparation of annular coated catalysts essentially (in
particular) when H is at least >0.5 E.

[0052]Overall, the total amount M of adhering pairs of coated catalyst
rings formed in the preparation of one production charge of annular
coated catalysts, based on the total weight of the production charge, is
≦5% by weight. Usually, M, on the same basis, is even ≦4,
or ≦3, or ≦2, or ≦1% by weight. In the case of
careful preparation of annular coated catalysts, M, on the same basis,
may even be ≦0.8% by weight, or ≦0.5% by weight, or
≦0.3% by weight, ≦0.2% by weight, or ≦0.1% by
weight. In general, M is, however, on the same basis, >0, usually
≧0.005 and frequently even ≧0.01% by weight.

[0053]Owing to the aforementioned comparatively low amounts of adhering
pairs of coated catalyst rings formed, no increased significance was
attributed to their presence in the use of production charges of annular
coated catalysts for the configuration of the fixed catalyst bed in the
reaction tubes of tube bundle reactors.

[0054]However, extremely careful investigations by the applicant with
regard to the configuration of fixed catalyst beds in reaction tubes of
tube bundle reactors using annular coated catalysts have led to the
result that, in the case of an unfavorable position of an adhering pair
of coated catalyst rings in the fixed catalyst bed disposed in a reaction
tube of a tube bundle reactor, the hotspot temperature in this reaction
tube can be increased perceptibly merely by the presence of a single
adhering pair of coated catalyst rings in the fixed catalyst bed.

[0055]However, an elevated hotspot temperature means accelerated aging of
the corresponding fixed catalyst bed charge of a reaction tube. In order
to compensate at least temporarily for such an accelerated aging process
with regard to the desired space-time yield of target product in a
heterogeneously catalyzed partial gas phase oxidation performed in a tube
bundle reactor, an accelerated increase of THin of the at least
one heat exchange medium is required, which in turn causes an additional
acceleration of the aforementioned aging process. The ultimate overall
effect which results is a reduced lifetime of the fixed catalyst bed
charge of the tube bundle reactor, which is undesired for the reasons
already described.

[0056]The presence of one (or else more) adhering pair(s) of coated
catalyst rings is particularly disadvantageous in the fixed catalyst bed
of a thermal tube. The profile of the reaction temperature within the
thermal tubes arranged in the tube bundle reactor to be representative of
all working tubes forms, as already stated, the basis for the control of
the overall operation of a tube bundle reactor (for example the control
of the loading of the fixed catalyst bed with reaction gas, the control
of the composition of the reaction gas mixture, the setting of the
particular THin etc).

[0057]In general, the control of the overall operation, for safety
reasons, is directed to those thermal tubes whose operating data are the
most marginal. When these operating data are representative of the
operating data of the corresponding working tubes only to a limited
degree owing to the presence of adhering pairs of coated catalyst rings
in the fixed catalyst bed of the corresponding thermal tubes, this
normally leads to the effect that the overall tube bundle reactor is not
operated in its optimal operating state.

BRIEF SUMMARY OF THE INVENTION

[0058]Against this background, it was an object of the present invention
to provide an improved process for charging the reaction tubes of a tube
bundle reactor with a fixed catalyst bed which is suitable for performing
a heterogeneously catalyzed partial gas phase oxidation of an organic
starting compound and which is configured using annular coated catalysts,
said process having the disadvantages of the prior art processes
described in reduced form at worst.

BRIEF DESCRIPTION OF THE DRAWINGS

[0059]FIG. 1 illustrates the geometric form of the screen orifice(s) being
a rectangle.

[0060]FIG. 2 illustrates the form of the screen orifice(s) being an
elongated hole.

[0061]FIG. 3 illustrates the form of the screen orifice(s) being an
irregular shape.

[0062]FIG. 4 illustrates the geometric form of the screen orifice(s) being
a parallelogram.

[0065]FIG. 7 illustrates a slotted sheet having orifices of an elongated
hole shape in a mutually offset arrangement.

[0066]FIG. 8 illustrates a slotted sheet having orifices of an elongated
hole shape in an overlapping offset arrangement.

[0067]FIG. 9 illustrates a slotted sheet having orifices of an elongated
hole shape in a straight line arrangement.

[0068]FIG. 10 illustrates a slotted sheet having rectangular orifices in a
straight line arrangement.

[0069]FIG. 11 illustrates a slotted sheet having orifices of an elongated
hole shape in a fishbone-like arrangement.

DETAILED DESCRIPTION OF THE INVENTION

[0070]Accordingly, a process has been found for introducing a portion
withdrawn from at least one production charge of annular coated catalysts
K into a reaction tube of a tube bundle reactor for the purpose of
charging this reaction tube with a fixed catalyst bed suitable for
performing a heterogeneously catalyzed partial gas phase oxidation of an
organic starting compound, which comprises, before the withdrawal of the
portion from the at least one production charge and/or after the
withdrawal or before the introduction of the portion withdrawn into the
reaction tube, removing adhering pairs of annular coated catalysts K
formed in the preparation of the at least one production charge of
annular coated catalysts K at least partly from the at least one
production charge and/or from the portion withdrawn.

[0071]Advantageously in accordance with the invention, before the
withdrawal of the portion from the at least one production charge of
annular coated catalysts K, adhering pairs of coated catalysts K formed
in the course of preparation thereof, based on the total content (on the
total amount) of adhering pairs of coated catalyst rings which are
present as a result of the preparation in the at least one production
charge, are removed from the at least one production charge to an extent
of at least 20% by weight, preferably to an extent of at least 30% by
weight, more preferably to an extent of at least 40% by weight and most
preferably to an extent of at least 50% by weight. It is even better
when, in the process according to the invention, before the withdrawal of
the portion from the at least one production charge of annular coated
catalysts K, adhering pairs of coated catalysts K formed in the
preparation thereof, based on the total content (on the total amount) of
adhering pairs of coated catalyst rings present as a result of the
preparation in the at least one production charge, are removed to an
extent of at least 60% by weight, or to an extent of at least 70% by
weight, preferably to an extent of at least 80% by weight or an extent of
at least 90% by weight, more preferably to an extent of at least 95% by
weight or to an extent of at least 98% by weight and most preferably to
an extent of 100% by weight.

[0072]It will be appreciated that it is also possible in accordance with
the invention only after (or additionally after) the withdrawal of the
portion from the at least one production charge of annular coated
catalysts K to withdraw (remove) adhering pairs of coated catalyst rings
present as a result of preparation in this withdrawn portion, based on
their total amount present in the portion withdrawn, to an extent of at
least 20% by weight, or to an extent of at least 30% by weight, or to an
extent of at least 40% by weight or to an extent of at least 50% by
weight, or to an extent of at least 60% by weight, or to an extent of at
least 70% by weight, or to an extent of at least 80% by weight, or to an
extent of at least 90% by weight, or to an extent of at least 95% by
weight and most preferably to an extent of 100% by weight, before this
portion is introduced into the reaction tube.

[0073]In principle, in heterogeneously catalyzed partial gas phase
oxidations, the fixed catalyst bed in each individual reaction tube may
consist only of the portion, essentially of equal size, withdrawn in each
case from the at least one production charge of annular coated catalysts
K.

[0074]It will be appreciated that the fixed catalyst bed, over the total
length of a reaction tube may, though, also consist of a homogenized
mixture of a plurality of (i.e. at least two) mutually distinguishable
types Si of geometric shaped catalyst bodies or of geometric shaped
catalyst bodies and geometric shaped inert bodies (i.e. such a mixture
may consist of at least two mutually distinguishable types of geometric
shaped catalyst bodies, or of a single type of geometric shaped catalyst
bodies and of a single type of geometric shaped inert bodies, or of at
least two types of mutually distinguishable geometric shaped catalyst
bodies and a single type of geometric shaped inert bodies, or of at least
two types of mutually distinguishable geometric shaped catalyst bodies
and at least two types of mutually distinguishable geometric shaped inert
bodies).

[0075]Among these mutually different types Si, it is possible, if
appropriate, for only one type of annular coated catalysts K relevant in
accordance with the invention to be present. Possible distinguishing
features of the mutually different types Si are the type of geometry, the
type of active composition, the type of the support material, etc.

[0076]In principle, useful materials for the geometric shaped inert bodies
(they serve the purpose of diluting geometric shaped catalyst bodies in a
fixed catalyst bed and in this way of restricting the local evolution of
heat in the fixed catalyst bed disposed in the reaction tube as the
reaction gas mixture flows through it) are the same materials which can
also be used for the inert (for example annular) shaped support bodies
for preparing coated catalysts and essentially do not intervene in the
course of the gas phase partial oxidation.

[0077]The latter means here generally that, when the reaction gas mixture,
under the same reaction conditions, is conducted through a reaction tube
charged only with inert shaped support bodies (inert shaped diluent
bodies), the conversion of the organic starting compound to be oxidized
partially is ≦5 mol %, usually ≦2 mol %.

[0079]In principle, all inert shaped support bodies are also useful as
geometric shaped inert bodies for diluting geometric shaped catalyst
bodies in a fixed catalyst bed.

[0080]Such a dilution allows the volume-specific activity of a fixed
catalyst bed, as already stated, to be adjusted specifically to the
requirement of the particular heterogeneously catalyzed partial gas phase
oxidation.

[0081]Geometric shaped inert bodies and geometric shaped catalyst bodies
in a homogenized mixture corresponding to the above preferably have the
same geometry or at least a similar geometry.

[0082]The wording "homogenized mixture" means that measures have been
taken in order to mix the mutually different types of geometric shaped
bodies (or the different longest dimensions within one type)
homogeneously with one another. Ideally, the homogeneous mixing along the
entire longitudinal section reaches the statistical average, also in
relation to the particular individual type.

[0083]In many cases, a reaction tube charge (a reaction tube filling) with
one fixed catalyst bed, though, also consists of a plurality of mutually
distinguishable longitudinal sections installed one on top of another (in
succession) (fixed catalyst bed (longitudinal) sections, catalyst bed
sections). In this case, each individual longitudinal section may be
configured uniformly over its length as has already been detailed for a
reaction tube charged uniformly over its total reaction tube length. At
the transition from one intrinsically homogeneous bed section to the next
intrinsically homogenous bed section, the configuration (composition) of
the bed normally changes abruptly. Along an individual reaction tube,
this gives rise to fixed catalyst bed sections which have a heterogeneous
structure. This is also referred to as a structured filling (or charge)
of the reaction tubes.

[0084]At the start (viewed in flow direction of the reaction gas flowing
through the reaction tube) and/or at the end of the reaction tube, the
fixed catalyst bed is frequently concluded by a sole bed of geometric
shaped inert bodies. Such sole inert beds are typically not included in
the fixed catalyst bed.

[0085]Appropriately from an application point of view, in the case of a
structured filling of the reaction tubes, the contents of an
intrinsically homogeneous bed section, following the teaching of DE-A 10
2004 023249, will be obtained beforehand in homogenized form and be
packaged as such a bed section portion. When annular coated catalysts K
are constituents of such a bed section portion packaged beforehand, they
are introduced in accordance with the invention into the reaction tube as
part of the corresponding bed section portion. In other words, for the
advance preparation of the bed section portion, the at least one
production charge of annular coated catalysts K (preferably in accordance
with the invention), once adhering pairs of coated catalyst rings which
have formed in the course of its preparation and are present therein as a
result have been removed at least partly from it in the inventive manner,
the required portion is withdrawn and homogenized with the other
geometric shaped bodies of the bed section portion, the resulting
homogenized mixture of geometric shaped bodies is introduced into the
packaging and the packing thus obtained, in the course of the charging of
the reaction tubes with the desired fixed catalyst bed, is emptied into
the reaction tube. In other words, the inventive introduction of a
portion withdrawn from at least one production charge of annular coated
catalysts K into a reaction tube of a tube bundle reactor need not
necessarily be effected separately, but can also be effected in a
homogenized mixture with other geometric shaped bodies (it will be
appreciated that the adhering bodies can also be removed only after the
withdrawal of a portion from the at least one production charge).

[0086]In general, the filling of a reaction tube with a structured fixed
catalyst bed is configured such that the volume-specific activity of the
fixed catalyst bed increases in flow direction of the fixed catalyst bed.

[0087]This can be realized, for example, in a simple manner by virtue of
the fixed catalyst bed consisting of mutually different longitudinal
sections which differ from one another merely in that one type of annular
coated catalysts K is diluted with different proportions of only one type
of shaped inert bodies. In flow direction of the reaction gas, the degree
of dilution with shaped inert bodies decreases, and the last longitudinal
section of the fixed catalyst bed in flow direction will frequently
consist only of annular coated catalysts K.

[0088]A volume-specific activity of the fixed catalyst bed increasing in
flow direction of the reaction gas can, however, also be realized by
virtue of the individual longitudinal sections of the fixed catalyst bed
consisting in each case only of one type of annular coated catalyst, the
ring geometries of the mutually different coated catalysts typically
being essentially the same, but the active compositions differ from one
another on the basis of a different elemental composition, with the
proviso that the catalytic activity of the active composition used in
each case increases in flow direction of the reaction gas mixture. The
volume-specific activity of an intrinsically homogeneous longitudinal
section of a fixed catalyst bed charge of a reaction tube is normally
increased when, with continuous charging of the reaction tube as in the
corresponding longitudinal section of the reaction tube under otherwise
identical reaction conditions (i.e. identical composition of the reaction
gas mixture, identical loading of the fixed catalyst bed charge with
reaction gas mixture and identical entrance temperature of the heat
carrier and identical flow conditions of the heat carrier), an increased
conversion of the organic starting compound to be oxidized partially
results.

[0090]The process according to the invention is of particular relevance
when the fixed catalyst bed introduced into the reaction tubes consists
of annular coated catalysts to an extent of at least 20%, or to an extent
of at least 30%, or to an extent of at least 40%, or to an extent of at
least 50%, or to an extent of at least 60%, or to an extent of at least
70%, or to an extent of at least 80%, or to an extent of at least 90%, or
to an extent of at least 95%, or to an extent of 100% of its weight.

[0091]Preferably in accordance with the invention, at least 20% by weight,
preferably at least 40% by weight, more preferably at least 60% by
weight, even more preferably at least 80% by weight and at best the
entirety of the annular coated catalysts present in a reaction tube are
introduced into the reaction tube by the inventive procedure.

[0092]Advantageously in accordance with the invention, the annular coated
catalysts introduced into the reaction tube by the inventive procedure
are especially those of a fixed catalyst bed disposed in a reaction tube
which, viewed in flow direction of the reaction gas mixture, are disposed
in the first 80%, or in the first 60%, or in the first 40%, or in the
first 20% of the total fixed catalyst bed (charge) length.

[0093]In principle, all statements made in this document with regard to
heterogeneously catalyzed partial gas phase oxidations of organic
starting compounds and their performance in a fixed catalyst bed disposed
in the reaction tubes of a tube bundle reactor apply in particular when
the reaction tubes have been charged with the fixed catalyst bed in the
inventive manner.

[0094]The steam content of the reaction gas input mixture in these
heterogeneously catalyzed partial gas phase oxidations may in principle
be 0 (vanishing).

[0095]Normally, the steam content of the reaction gas input mixture in
these heterogeneously catalyzed partial gas phase oxidations will
normally, however, be >0% by volume. Frequently, the steam content of
the reaction gas input mixture will be from ≧0.1 to 60% by volume,
or from ≧0.2 to 50% by volume or from ≧2 0.3 to 40% by
volume, or from ≧0.4 to 30% by volume, or from ≧0.5 to 25%
by volume, or from ≧0.75 to 20% by volume, or from ≧1 to
15% by volume, or from ≧2 to 10% by volume. Owing to its
comparatively elevated specific heat capacity, steam is generally an
excellent inert diluent gas for heterogeneously catalyzed partial gas
phase oxidations of organic starting compounds and in many cases has a
beneficial effect on the catalyst activity.

[0096]Useful sources for the molecular oxygen required in the reaction gas
input mixture for a heterogeneously catalyzed partial gas phase oxidation
include air, pure molecular oxygen, air depleted in molecular oxygen or
other mixtures of inert gas and molecular oxygen.

[0097]The content in the reaction gas input mixture of the organic
starting compound to be oxidized partially under heterogeneous catalysis
may, in heterogeneously catalyzed partial gas phase oxidations for which
the process according to the invention is relevant (i.e. especially all
heterogeneously catalyzed partial gas phase oxidations discussed in this
document), be up to 50% by volume or more.

[0098]Frequently, this content will be from ≧2 to 20% by volume, or
from ≧4 to 12% by volume.

[0099]When the reaction gas input mixture comprises the molecular oxygen
in a substoichiometric amount based on the desired partial oxidation, the
excess amount present in the reaction gas input mixture of the organic
starting compound to be oxidized partially may in principle function as
an inert diluent gas. When the reaction gas input mixture comprises
molecular oxygen in a superstoichiometric amount based on the partial
oxidation, it will, appropriately in accordance with the application, be
selected such that the composition of the reaction gas input mixture is
outside the explosive composition range.

[0100]It will be appreciated that the composition of the reaction gas
input mixture may, though, also be within the explosive composition
range, as is normally the case, for example, in the case of preparation
of phthalic anhydride from o-xylene and/or naphthalene.

[0101]On the grounds of a very long catalyst lifetime, the proportion of
the molecular oxygen in the reaction gas input mixture of a
heterogeneously catalyzed partial gas phase oxidation for which the
process according to the invention is relevant will generally preferably
be selected such that the product gas mixture of the gas phase partial
oxidation still comprises excess molecular oxygen (for example up to 3%
by volume).

[0102]The volume flow rate of the heating medium (of the at least one heat
exchange medium (preferably a liquid heat exchange medium)) in the
reaction tube surrounding space in gas phase partial oxidations relevant
in accordance with the invention is typically such that the temperature
rise (caused by the exothermicity of the partial oxidation) of the
(preferably liquid) at least one heat exchange medium, from its entry
point into the tube bundle reactor up to its exit point from the tube
bundle reactor, is from ≧0 to 15° C., or from ≧0 to
10° C., frequently from ≧2 to 8° C., preferably from
≧3 to 6° C.

[0103]The loading of the fixed catalyst bed with the organic starting
compound to be oxidized partially in a gas phase partial oxidation
relevant in accordance with the invention will generally be ≧50 l
(STP)/lh, usually ≧75 l (STP)/lh, in many cases ≧100 l
(STP)/lh. Usually, this loading will, however, be ≦600 l (STP)/lh.

[0104]The loading of the fixed catalyst bed with reaction gas input
mixture in a gas phase partial oxidation relevant in accordance with the
invention will frequently be ≧1500 l (STP)/lh, or ≧2000 l
(STP)/lh, or ≧2500 l (STP)/lh, or ≧3000 l (STP)/lh, or
≧4000 l (STP)/lh. In general, the aforementioned loading in such
heterogeneously catalyzed partial gas phase oxidations will, however, be
at values of ≦6000 l (STP)/lh, or ≦5000 l (STP)/lh. The
conversion of the organic starting compound to be oxidized partially
will, in gas phase partial oxidations relevant in accordance with the
invention, typically be ≧50 mol %, frequently ≧70 mol %, in
many cases ≧80 mol % and often ≧90 mol % (based on single
pass of the reaction gas mixture through the fixed catalyst bed). The
selectivity of target product formation will typically be ≧70 mol
%, frequently ≧80 mol % and in many cases ≧90 mol %.

[0105]Otherwise, the boundary conditions of a heterogeneously catalyzed
partial gas phase oxidation relevant in accordance with the invention
will, appropriately in accordance with the application, overall, normally
be selected such that the temperature difference between the hotspot
temperature of the reaction gas mixture in the individual reaction zones
(temperature zones) of the tube bundle reactor and the particular
accompanying THin of the temperature zone, even in long-term
operation, generally does not exceed 100° C. In partial oxidations
with exothermicity which is not so pronounced, this temperature
difference, even in long-term operation, will frequently be
≦80° C. or ≦70° C., and is in many cases from
20 to 70° C. or to 50° C.; this temperature difference,
even in long-term operation, is preferably low.

[0106]Moreover, the aforementioned boundary conditions are typically
selected such that the "peak-to-salt temperature sensitivity" (cf.
definition in EP-A 1106598), especially also in long-term operation, is
≦9° C., but ≦7° C., or ≦5° C.,
or ≦3° C. Among other factors, this also takes account of
the fact that the temperature of the at least one heat exchange medium,
viewed over the cross section of the tube bundle reactor, is generally
not completely homogeneous (uniform), but rather has a slight gradient.

[0107]The external diameter E of the annular shaped support bodies of
coated catalysts K to be introduced into a reaction tube in accordance
with the invention is typically from 4 to 10 mm, the accompanying height
(length) H is from 2 to 10 mm and their wall thickness is generally from
1 to 4 mm.

[0108]The external diameter E of such annular shaped support bodies is
preferably from 4 to 8 mm, the wall thickness from 1 to 2 mm and the
height H from 3 to 7 mm.

[0110]The thickness of the active composition coating applied to the
annular shaped support body is generally from 10 to 3000 or to 1000
μm, preferably from 10 to 500 μm, frequently from 100 to 500 μm
and in many cases from 200 to 300 μm.

[0111]The catalytic active composition applied to the annular shaped
support bodies in the case of coated catalysts K is generally at least
one multielement oxide (frequently at least one metal oxide) or
compositions which comprise at least one multielement oxide (for example
multimetal oxide).

[0112]In principle, the term "multielement oxide" in this document means
that the catalytically active oxide composition, as well as oxygen, also
comprises at least two further, different elements. Particularly
frequently, the catalytically active multielement oxide compositions used
are those which have at least two metallic elements, especially at least
two transition metal elements. In this case, reference is made to
multimetal oxide compositions. In general, catalytically active
multielement oxide compositions are not simple physical mixtures of
oxides of their elemental constituents, but rather heterogeneous mixtures
of complex poly compounds of these elements. In principle, useful
catalytically active multielement oxide compositions also include,
however, simple physical mixtures (for example agglomerates of finely
divided element oxides) of oxides of their elemental constituents (for
example in the case of the annular coated catalysts K for preparing
phthalic anhydride from o-xylene and/or naphthalene), which is why the
generic term "multielement oxide compositions" in this document is
intended to encompass such mixtures (agglomerates).

[0113]In a multitude of cases, the at least one catalytically active
multielement oxide is one which comprises

[0114]In addition, useful coated catalysts to be introduced into a
reaction tube in accordance with the invention are those which comprise,
as an active composition, elemental silver on an oxidic annular shaped
support body.

[0115]A removal of adhering pairs of annular coated catalysts K formed in
the preparation of the at least one production charge of annular coated
catalysts K from the at least one production charge can be effected
manually in the simplest manner, i.e. by manual sorting. Alternatively,
the removal can also be undertaken by wind sifting, in which the
different weight of coated catalysts K and their adhering pairs is
exploited.

[0116]For example, the entirety or a portion of the at least one
production charge can be conducted through a lock which opens only to
admit a single coated catalyst ring K (the detection can be effected, for
example, by means of optical methods). When the lock is subsequently
blocked by an adhering pair, it is blown away by an appropriately
directed gas stream (for example an air stream) (i.e. the lock entry is
unblocked by blowing). Beyond the lock, annular coated catalyst K can
then be withdrawn for introduction into a production tube.

[0117]Particularly advantageously from an application point of view, a
removal of adhering pairs of annular coated catalysts K formed in the
preparation of the at least one production charge of annular coated
catalysts K will, however, be undertaken by a screening process. In this
process, the screen residue which remains (also known as "oversize") is
normally essentially the adhering pairs (and any other multiple annular
coated catalysts K formed in the course of preparation of the annular
coated catalysts K), while the material passing through the screen (also
known as "undersize") typically comprises essentially the annular coated
catalysts K.

[0118]When, for the annular geometry E×I×H of the coated
catalyst K (E=external diameter, I=internal diameter, H=height), the
relationship H≦0.5E applies, the formation of fused adhering pairs
of coated catalyst rings in the preparation of the annular coated
catalysts K is, according to the investigations of the applicant,
generally quantitatively negligible with most customary binders compared
to the formation of tandem adhering pairs of coated catalyst rings.

[0119]Against this background, for the inventive removal of adhering pairs
from the at least one production charge of aforementioned annular coated
catalysts K (or from the portion withdrawn therefrom), an advisable
process for screening is one with the aid of a screen which has screen
orifices O1 within whose continuous outline a rectangle R with the
side lengths L and C can be inscribed with the proviso M1,

L>E≧2H>C>H,

but not with the proviso M1*,

L>C≧2H.

[0120]Preferably, in the case of the aforementioned annular coated
catalysts K, an advisable process for screening is one with the aid of a
screen which has screen orifices O2 within whose continuous outline
a rectangle R with the side lengths L and C can be inscribed with the
proviso M2,

L>E≧2H>1.75H≧C≧1.25H,

but not with the proviso M2*,

L>C>1.75H.

[0121]Both in the case of the screen orifices O1 and in the case of
the screen orifices O2, it is favorable in accordance with the
invention when L≧1.05E, better ≧1.1E, preferably
≧1.25E, more preferably ≧1.5E and most preferably
≧1.75E.

[0122]In principle, both in the case of the screen orifices O1 and in
the case of the screen orifices O2, L≧2 E, or ≧2.5E.
In general, L will, however, both in the case of the screen orifices
O1 and in the case of the screen orifices O2, be ≦20E,
in many cases ≦15E, frequently ≦10E and often ≦5E.
However, this length restriction is frequently caused by secondary
features, for example an outstanding mechanical stability of the screen,
rather than by the screening action desired.

[0123]In the case that, in the aforementioned cases, a screening removal
of fused adhering pairs is additionally desired, the following conditions
should be satisfied for the proviso M1:

2E>L>E≧2H>C>H,

preferably even

1.9E>L>E≧2H>C>H,

and the following conditions should correspond and may be satisfied for
the proviso M2:

2E>L>E≧2H>1.75H≧C≧1.25H,

and preferably even

1.9E>L>E≧2H>1.75H≧C≧1.25H.

[0124]Appropriately from an application point of view, both the continuous
outline of the screen orifices O1 and the continuous outline of the
screen orifices O2 are a rectangle with the side lengths L and C (in
simplified language, this document frequently refers to the geometric
form of the continuous outline of a screen orifice as the "geometric form
of the screen orifice"), as shown by FIG. 1.

[0125]It will be appreciated that both a screen orifice O1 and a
screen orifice O2 may, though, also be an elongated hole, as shown
by way of example by FIG. 2.

[0126]The geometry of such an elongated hole derives from that of the
relevant rectangle with the side lengths L and C in a simple manner by
virtue of the rectangle sides with the length C each being replaced by a
semicircle with the diameter C (the hole width), the semicircular curve
pointing outward from the rectangular area. A comparatively general form
of a possible screen orifice (or its outline) which is suitable in
accordance with the invention in the sense described above is shown by
way of example by FIG. 3. Of course, another possible screen orifice (or
its outline (both expressions are, as already stated, used in an
equivalent manner in this document)) suitable in accordance with the
invention in the sense described above is a parallelogram, as shown by
way of example in FIG. 4. In addition, another useful outline of a screen
orifice suitable in accordance with the invention in the sense described
above is one which derives from a rectangular outline by virtue of all or
at least some of the corners of the rectangle having been rounded off.

[0127]When, for the annular geometry E×I×H of the annular
coated catalyst K, the relationships E≧H>0.5E apply, the
formation of fused adhering pairs of coated catalyst rings in the
preparation of annular coated catalysts K, according to the
investigations of the applicant, becomes increasingly significant with
increasing H/E ratio (depending on the binder used).

[0128]Against this background, a recommended process for the inventive
removal of adhering pairs from the at least one production charge (or
from the portion withdrawn therefrom) of such (aforementioned) annular
coated catalysts K is a process for screening with the aid of a screen
which has screen orifices O3 within whose continuous outline a
rectangle R with the side lengths L and C can be inscribed with the
proviso M3,

L>E<2H>C>H,

but not with the proviso M3*,

L≧C≧2H.

[0129]In the case of the aforementioned annular coated catalysts K, a
recommended process is preferably a process for screening with the aid of
a screen which has screen orifices O4 within whose continuous
outline a rectangle R with the side lengths L and C can be inscribed with
the proviso M4,

2E>L>E<2H>C>H,

but not with the proviso M4*,

L≧C≧2H.

[0130]More preferably, a recommended process in the case of the
aforementioned annular coated catalysts K is a process for screening with
the aid of a screen which has screen orifices O5 within whose
continuous outline a rectangle R with the side lengths L and C can be
inscribed with the proviso M5,

2H>L>E<2H>C>H,

but not with the proviso M5*,

L≧C≧2H.

[0131]Preferably in accordance with the invention, the rectangles R to be
inscribed into the screen orifices O3, O4 or O5 are its
special form of a square where L=C. The latter is found to be beneficial
especially for the screen throughput.

[0132]Appropriately from an application point of view, the continuous
outlines of the screen orifices O3, O4 and O5 are also
each a rectangle with the side lengths L and C (preferably its special
form of a square where L=C).

[0133]It will be appreciated that a screen orifice O3 or O4 or
O5 may also be an elongated hole (which may also be derived here
from a square). Of course, a parallelogram is also possible as such an
outline, or a rectangle of whose corners all or at least some have been
rounded off.

[0134]In principle, a screen to be used in accordance with the invention
may, for example, have a plurality of different types of screen orifices
possible in accordance with the invention. Advantageously in accordance
with the invention, a screen used in a process according to the invention
will, however, have not more than three, and generally not more than two,
different types of screen orifices which satisfy the inventive profile of
requirements. Very particularly advantageously, a screen to be used in
accordance with the invention will, however, have only one type of
inventive screen orifices.

[0135]The term "screen" is used in this document synonymously with the
term "screen plate". Otherwise, the term "screen" or "screen plate" is
used in this document in the sense of the definition given in EP-A 1 726
358 in column 5 lines 48 to 57.

[0136]In other words, the screen plate may, for example, be configured as
a grid or grille, as a perforated or slotted sheet (i.e. as a sheet with
punched, lasered, water-cut or milled screen orifices) or as a screen
fabric (it consists of wires woven together, and the wires may be round
or profiled).

[0137]In principle, for a screening process according to the invention,
useful screen plate variants are also any other screen plate variants
detailed in Aufbereitungs-Technik-No. 11/1960, p. 457 to 473 or in
Chem.-Ing.-Techn. 56 (1984) No. 12, page 897 to 907. It will be
appreciated that it is also possible to use, for a screening process
according to the invention, all screen plates detailed in "Sieben und
Siebmaschinen, Wiley-VCH GmbH & Co. KGaA, Paul Schmidt et al (2003)"
according to the invention.

[0138]Grids or grilles and screen fabrics (both ensure particularly high
specific screen outputs in kg/m3 h at high efficacy) are suitable
especially in the case of screen plates having only one inventive type of
rectangular screen orifice. An exemplary illustrative depiction of such a
screen fabric is shown by FIG. 5 of this document.

[0139]An exemplary illustrative depiction of such a grid or grille is
shown by FIG. 6 of this document.

[0140]Any screen orifices suitable in accordance with the invention (or
outlines of screen orifices) can be realized in a simple manner in
perforated or slotted sheets. However, perforated or slotted sheets
advantageous in accordance with the invention are especially those which
have only one type of rectangular (or square) screen orifice (or outline
thereof) or a screen orifice (or outline thereof) having an elongated
hole shape.

[0141]What is particularly advantageous about perforated or slotted sheets
is that the relative arrangement of screen orifices suitable in
accordance with the invention is possible in virtually any manner. When
the slotted sheet has only one type of rectangular (or square) screen
orifice or a screen orifice having an elongated hole shape useful
relative arrangements thereof in the slotted sheet for the process
according to the invention are especially the mutually offset screen
orifice arrangement according to FIG. 7, the overlapping offset screen
orifice arrangement according to FIG. 8 (which is very particularly
preferred in accordance with the invention (for reasons of stability
among others)), the screen orifice arrangement in straight lines
according to FIGS. 9 and 10, or fishbone-like screen orifice arrangements
according to FIG. 11. A reason for a further advantage of slotted sheets
is that they can be cleaned more easily in the case of product switches
and are less prone to blockage of the screen orifices by stuck particles.
They also generally have a higher mechanical stability.

[0142]Otherwise, perforated sheet screens (and slotted sheet screens)
suitable in accordance with the invention can be configured as described
in DIN 24041.

[0143]Typical sheet thicknesses d of perforated sheet screens (or slotted
sheet screens) usable in accordance with the invention are from 1 to 5
mm, preferably from 1 to 3 mm, more preferably from 2 to 3 mm.

[0144]The open screen area F (the total (cross-sectional) area of all
screen orifices present in a slotted sheet screen plate) of slotted sheet
screen plates favorable in accordance with the invention will, based on
the total area of the slotted sheet screen plate, typically be from 10 to
60%, preferably from 20 to 50% and more preferably from 30 to 50%.

[0145]A sheet with elongated holes suitable in accordance with the
invention (a screen plate with elongated holes suitable in accordance
with the invention) with mutually offset elongated holes according to
FIG. 7 may, for example, have the following configuration variants:

[0149]In the case of annular coated catalysts K of geometry
E×I×H=7 mm×4 mm×3 mm, suitable screens for an
inventive screening-off of adhering pairs of coated catalyst rings are,
for example, screens with elongated holes of the type described above
(especially with an overlapping offset screen orifice arrangement) with
C=5.50 mm and L=14.1 mm.

[0150]The sheet thickness may, for example, be 2.2 mm.

[0151]The bridge width a between elongated holes is, appropriately from an
application point of view, 4.0 mm, and the distance b between two
successive elongated holes on a common longitudinal line is
advantageously 5.0 mm. The open screen area F is in this case 36.5%.

[0152]In the performance of an inventive screening-off, the material being
screened is transported through a screen plate suitable in accordance
with the invention, advantageously in accordance with the invention
parallel to the preferential direction L of the inventive screen
orifices. In a corresponding manner, the material being screened is also
applied to the screen (to the screen plate) with this direction of
application.

[0153]When the screen plate used in accordance with the invention is a
perforated sheet with punched screen orifices, the punched burr is
generally removed and the outline of the screen orifices is,
appropriately from an application point of view, rounded off. Over the
screen plate thickness, the cross section of a screen orifice is normally
essentially constant (i.e. the orifice generally has a constant passage
cross section). When the punched burr is not removed, it normally points
in the direction of the screen passage.

[0154]In principle, the material being screened can be transported through
the screen in a screening process according to the invention through a
circular, elliptical and/or linear vibrating motion of the screen plate.
For this purpose, for a screening process according to the invention, it
is possible in principle to use all screening machines recommended, for
example, in Chem.-Ing.-Tech. 56 (1984) No. 12, p. 897 to 907, and also in
Sieben und Siebmaschinen, Grundlagen und Anwendung [Screens and Screening
Machines, Fundamentals and Use], Wiley VCH, Paul Schmidt (2003). Also
useful for a screening process according to the invention are the
screening machines of the multideck design described in the documents
DE-A 3520614, EP-A 205089 and DE-A 3431337, and those described in
Aufbereitungstechnik 42 (2001) No. 7, page 345 to 348 and in
Aufbereitungstechnik 41 (2000) No. 7, page 325 to 329.

[0155]A group of screening machines suitable for performing a process
according to the invention is that of the planar screens in which the
material being screened slides as a mat of material being screened in a
linear or circular motion on the screen (the screen plate). The intrinsic
weight and the friction against the screen cause shearing of the mat of
material being screened. What is advantageous is the very low backmixing,
which usually has an adverse effect.

[0156]The vibrating motion of the screen surface in the case of planar
screens is effected in their screen plane. The vibrating motion may have
a linear (to and fro) or circular profile (in the first case, reference
is made to a linear planar vibrating screen). In the former case, it can
proceed in conveying direction or transverse to it. Asymmetric
acceleration in the case of linear vibrating motion in conveying
direction, even in the case of a horizontal screen, can bring about
longitudinal transport of the material being screened.

[0157]The circular vibration offers the advantage of constantly
maintaining optimal acceleration. It will be appreciated that it is also
possible to employ a combination of linear and circular vibrators in the
process according to the invention.

[0158]In circular vibrators, the horizontal circulating motion is
frequently generated through a geared motor. In linear vibrators, the
whole screen frame (in which the screen plate is normally quite generally
mounted) is set into a linear motion by contrarotatory unbalanced masses.
Linear vibrators may be employed either with a horizontal or inclined
screen plate. In the case of a inclined screen plate, the material being
screened, by virtue of appropriate inclined inclination of the plane of
vibration relative to the screen plate, in accordance with a parabolic
trajectory, is thrown upward and simultaneously forward. The angles of
inclination may, for example, be from -3° to 25°. From
3° to 4° are preferred in accordance with the invention.
Suitable in accordance with the invention are, for example, linear
vibration screens from Rhewurm GmbH in Remscheid, Germany.

[0159]Rectangular screening machines are generally preferred over round
screens for an inventive planar screening operation. In the case of
these, normally rectangular screen plates are introduced into a likewise
rectangular screen frame.

[0160]Advantageously, for an inventive screen removal, an arrangement of
screen plates one on top of another is employed, as is customary, for
example, in the case of the screening machines of the multideck design
already mentioned.

[0161]In this case, appropriately in accordance with the invention, the
adhering pairs of coated catalyst rings (and any other multiple coated
catalyst rings) will, in the inventive manner, be removed at least partly
as screen residue with the uppermost screen. The desired coated catalyst
rings K and any more finely divided constituents of the material being
screened compared to the coated catalyst rings K are, in contrast, passed
through from the uppermost screen plate to the screen plate below. Its
screen orifices may, for example, following the teaching of U.S. Pat. No.
7,147,011 and of EP-A 1726358, be configured such that the coated
catalyst rings K form the screen residue (the oversize) and the finely
divided constituents of the material being screened form the material
which passes through the screen (the undersize). Alternatively to the
teaching of U.S. Pat. No. 7,147,011 and of EP-A 1726358, with regard to
an annular coated catalyst K with the geometry E×I×H with the
proviso that E≧H and with the aim of obtaining the annular coated
catalysts K as oversize, it is also possible for the screen orifices of
the screen plate to be configured such that their continuous outline has
in each case at least two straight-line sections which are opposite one
another at a distance C* over at least one length L* like two parallel
sides of a rectangle with the side lengths L* and C*, with the proviso
that each parallel line, running through an outline point P lying on the
outline of a screen orifice, to the theoretical rectangle side with the
side length C* does not have any further point lying on the outline whose
distance from the outline point P is >C* and, at the same time, the
relations L*>E≧H>C*≧(E-I)/2 are satisfied.

[0162]In the case of a successive arrangement of screen plates, both round
screens and rectangular screens can be used. The vibrating motion is
preferably configured such that the screen residue is in each case
transported to the periphery of the round screen or rectangular screen
and discharged there.

[0163]In the case of an inventive use of screening machines of the
multideck design already addressed, a Mogensen Sizer® will
advantageously be employed.

[0164]The system of a Mogensen--(for example one of the "SZ 0534" type
suitable for an inventive removal, on a 04711 machine, built in 1997)
consists of at least two normally differently inclined screen decks which
are arranged one on top of another with screen orifices decreasing in the
downward direction and increasing angles of inclination (to the
horizontal). In general, the angle of inclination is in the range from 5
to 300. For the inventive requirements, the use of a Mogensen Sizer with
two screen decks is typically sufficient. The upper of the two screen
decks accomplishes the inventive removal of adhering pairs and the screen
deck which follows below it can remove the annular coated catalysts K
from more finely divided constituents of the material being screened as
screen oversize. Caused by the different inclination of the screen plates
(screen linings), their screen orifices act like screen orifices of a
smaller size. Therefore, compared to flat screens, the screen orifices
can be selected with a comparatively larger size with essentially equally
good separating efficiency, which enables increased specific screen
outputs. It is characteristic of a Mogensen Sizer that the material being
screened is initially loosened up and then flows through the individual
screen decks almost vertically in free fall. The coarse fractions
obtained are each collected in an outlet of the sizer and conducted out
of the sizer via an outlet stub assigned to the outlet. Comprehensive
details of Mogensen Sizers can be found, for example, in
Aufbereitungstechnik 42 (2001) No. 7, page 345 to 348, and in
Aufbereitungstechnik 41 (2000) No. 7, page 325 to 329, and the literature
cited in these two documents, but also in DE-A 3520614, EP-A 205089 and
in DE-A 3431337.

[0165]In the preparation of annular coated catalysts K with an annular
geometry E×I×H=8 mm×5 mm×6 mm, it is possible,
for example, for the inventive removal of adhering pairs to use a
two-deck Mogensen Sizer of the SZ 0534 type (machine 04711) with two
rectangular screen decks (e.g. length 1340 mm and width 490 mm). The
distance between the two screen plates lies in the vertical, for example
at a maximum value of 130 mm. The screens used are, in a manner
appropriate in accordance with the invention, screening fabric according
to FIG. 5, but with square screen orifices in the case of the upper
screen deck (the geometry of the outline of the screen orifices of the
upper screen deck is advantageously 10 mm×10 mm and the geometry of
the outline of the screen orifices of the lower screen deck is
advantageously 6 mm×130 mm; the thickness of the woven steel wire
is typically from 1.5 to 1.7 mm; the inclination of the upper screen
plate to the horizontal is appropriately 100 and that of the lower screen
plate appropriately 200; typical throughputs of material being screened
are from 300 to 350 kg/h; later in this document, such a Mogensen Sizer
is also referred to as a "Mogensen Sizer I").

[0166]When the annular coated catalysts K prepared have the annular
geometry E×I×H=7 mm×4 mm×7 mm, it is possible for
an inventive removal of adhering pairs to use a correspondingly
constructed Mogensen Sizer. The geometry of the outline of the screen
orifices of the upper screen deck is, however, advantageously 8
mm×8 mm and the geometry of the outline of the screen orifices of
the lower screen deck is advantageously 5 mm×130 mm. This Mogensen
Sizer shall be referred to in this document as "Mogensen Sizer II".

[0167]While, in the case of an inventive removal with the aid of a
Mogensen Sizer, no screening assistant introduced between the two screen
decks is used in order to keep the upper and the lower screen plate
continuously free of stuck particles, it is generally appropriate in the
case of a predominantly horizontal screen surface to use rubber ball
knocking for this purpose (cf. FIG. 12 in Chem.-Ing. Tech. 56 (1984) No.
12, page 902). In this method, rubber balls are placed onto a blank plate
which is at a distance Z of 1.2- to 1.5 times the rubber ball diameter
below the actual screen (screen plate). The rubber balls, even in the
case of planar screening machines, jump from below against the screen and
clean it locally during the screening operation (during the screening).
Their elasticity is advantageously such that they essentially do not
cause any fracture of the material being screened. The blank plate is
usually a perforated sheet with preferably square hole orifices. In each
case, the hole orifices of the blank plate are such that the material
passing through the screen can pass through it.

[0168]Advantageously from an application point of view, screen plates (as
the "top plane") and blank plates (as the "base plane") are equipped with
identical cross-sectional area and are supplemented by four side walls of
height Z to form a cuboidal side insert which can be inserted in a simple
manner into the screen frame (the frame height projects beyond the screen
insert inserted generally by about 10 cm). Alternatively to rubber ball
knocking, screen cleaning can also be brought about during the screening
operation by means of flat or roller brushes arranged above and/or below
the screen plate.

[0169]The preparation of annular coated catalysts K and an inventive
screen removal can be performed either spatially separately or spatially
merging directly into one another. The latter is appropriate, for
example, when the preparation of the annular coated catalysts K is
effected as described in DE-A 2909671, DE-A 102005010645, EP-A 714700,
DE-A 10325488, DE-A 10360058, WO 2004/108267 and German application
102007010422.9.

[0170]In these preparation processes, the annular shaped support body is
first moistened with a liquid binder, then a layer (coating) of the
aforementioned finely divided composition is adhered on the surface of
the moistened annular shaped support body by contacting with finely
divided, dry catalytic active composition (for example multielement oxide
composition) and/or finely divided dry precursor composition of the
catalytic active composition, and then the liquid binder is at least
partly volatilized from the annular shaped support body coated with the
finely divided composition under the action of heat, and any precursor
composition present in the coating is converted to the active composition
by thermal treatment. In this document, this preparation method is
referred to as the "coating process".

[0171]Useful liquid binders are in particular all of those which are
detailed in DE-A 10 2005 010645 and in EP-A 714700.

[0172]These include in particular inorganic and organic liquids, and also
mixtures of inorganic and organic liquids.

[0174]Preferred liquid binders are solutions which consist of water to an
extent of from 20 to 90% by weight and of an organic compound dissolved
in water to an extent of from 10 to 80% by weight. The organic proportion
in the aqueous solution to be used as a binder is preferably from 10 to
50% by weight, more preferably from 20 to 30%. Suitable organic
components of liquid binder are in particular mono- and polyhydric
organic alcohols such as glycol, 1,4-butanediol, 1,6-hexanediol and
glycerol, mono- or polybasic organic carboxylic acids such as propionic
acid, oxalic acid, malonic acid, glutaric acid and maleic acid, amino
alcohols such as ethanolamine or diethanolamine, mono- or polyfunctional
organic amides such as formamide, or monosaccharides and oligosaccharides
such as glucose, fructose, sucrose or lactose. One reason for the
advantageousness of such solutions as a liquid binder is that they are
generally capable of wetting both the annular support bodies and the
finely divided composition to be applied to them. Useful materials for
the annular shaped support bodies include all materials mentioned in this
document and all of those mentioned in German application 102007010422.9,
in DE-A 10 2005 010 645 and in EP-A 714 700. These include especially
aluminum oxide, silicon dioxide, silicates such as clay, kaolin,
steatite, pumice, aluminum silicate and magnesium silicate, silicon
carbide, zirconium dioxide and thorium dioxide.

[0175]Advantageously, the surface of the annular shaped support body is
rough (as recommended in the three documents above), since an increased
surface roughness generally causes an increased adhesion strength of the
coating of active composition and/or precursor composition applied on the
surface of the annular shaped support body.

[0176]Furthermore, the support material is preferably nonporous (total
volume of the pores based on the volume of the support body ≦1% by
volume).

[0177]For a performance of the above-described process for preparing
annular coated catalysts K, a suitable process principle is in particular
that disclosed in DE-A 2909671 (see also EP-A 714 700 and DE-A 10 2005
010 645) using the liquid binder desired in each case.

[0178]In other words, the annular shaped support bodies to be coated are
filled into a preferably inclined (the angle of inclination is generally
from 30 to 90°) rotating vessel (for example rotating pan or
coating tank or coating drum). Favorable rotary vessels for this end use
are especially the Hi-Coater HCF-100 from Freund Industrial Co., Ltd,
Tokyo (Japan) and the Hi-Coater LH 100 from Gebruder Lodige Maschinenbau
GmbH, Paderborn, Germany.

[0179]The rotating vessel conducts the annular shaped support bodies under
two metering devices which are arranged in succession at an advantageous
distance. The first of the two metering devices corresponds appropriately
to a nozzle by which the annular shaped support bodies rolling in the
rotating pan (Hi-Coater) are moistened in a controlled manner with the
liquid binder. The second metering device is, appropriately from an
application point of view, disposed outside the atomization cone of the
sprayed liquid binder and serves to supply the finely divided active
composition (for example a finely divided multielement oxide active
composition) and/or the finely divided precursor composition (for example
by means of a shaking channel). The annular shaped support bodies
moistened in a controlled manner take up the finely divided composition
(the finely divided powder) supplied, which is compacted by the rolling
motion on the outer surface of the annular shaped support body to form a
coherent coating (such a compacting motion does not take place in the
inner circle of the annular shaped support bodies, which is why it
remains essentially uncoated).

[0180]If required, the annular shaped support body base-coated in this
way, in the course of the subsequent rotation, again passes through the
spray nozzle, is moistened in a controlled manner (if appropriate with
another liquid binder) as it does so, in order to be able to take up a
further layer of (an optionally different) finely divided active
composition and/or precursor composition in the course of the further
motion, etc. (intermediate drying is generally not required). The at
least partial removal of the liquid binder used can, for example,
following the teaching of EP-A 714 700 or the teaching of DE-A 10 2005
010 645, be effected by final heat supply, for example by the action of
hot gases such as N2 or air (these are supplied and removed through
spatially separately mounted wall elements, configured in a mesh-like
manner, of the rotary pan, of the coating tank or of the coating drum (in
general, rotary vessel)).

[0181]What is of significance for the embodiment of the coating process
described is that the moistening of the annular shaped support bodies to
be coated is undertaken in a controlled manner. In short, this means that
the support surface is appropriately moistened such that it has adsorbed
liquid binder, but it does not appear visually on the support surface.
When the shaped support body is too moist, the finely divided active
composition and/or precursor composition agglomerates to form separate
agglomerates instead of attaching to the surface. More detailed
information on this subject can be found in DE-A 2909671, in EP-A 714 700
and in DE-A 10 2005 010 645. The latter is especially also true for the
final at least partial removal of the liquid binder used. This is because
a further advantage of the procedure described consists in the ability to
undertake this removal in a comparatively controlled manner, for example
by evaporation and/or sublimation. In the simplest case, this can, as
already stated, be effected through the action of hot gases of
appropriate temperature (frequently from 50 to 150° C.). Such an
action of hot gases can bring about either complete drying or only a
pre-drying. The end drying can then be effected, for example, in a drying
device of any type (for example in a conveyor belt drier) and/or not
until within the fixed catalyst bed of the tube bundle reactor, as
recommended, for example, by DE-A 10 2005 010 645.

[0182]The transition to an inventive removal of adhering pairs by
screening can be configured in a simple manner, for example as follows.
The production charge of annular coated catalyst disposed in the rotary
vessel can be emptied through a funnel by opening an emptying flap
disposed above the funnel. The discharge of the funnel is then continued
directly into a (discharge) tube slightly inclined relative to the
horizontal (the angle of inclination may, for example, be from -3°
to 25°; from 3° to 5° are preferred).

[0183]The discharge tube typically has a length of 1200 mm and an internal
diameter of, for example 100 mm. Otherwise, it is configured as a linear
vibratory screen. For this purpose, it comprises an installed screen
plate which extends over the entire tube length and divides the tube
interior into an upper half-tube (above the screen plate) and into a
lower half-tube (below the screen plate). As a result of tumbling motions
of the rotary vessel, the production charge present in the rotary vessel
empties into the upper half-tube of the discharge tube comprising the
screen plate.

[0184]In the discharge tube, it is transported to its end (typically: 80
kg of coated catalyst rings per 30 minutes). On the route of the
production charge through the discharge tube, the inventive removal of
adhering pairs takes place by means of the screen plate of the discharge
tube. The desired annular coated catalysts K form the material which
passes through the screen, while the adhering pairs removed are
discharged from the upper half-tube at the end thereof.

[0185]When the annular coated catalysts K are those of geometry
E×I×H=7 mm×4 mm×3 mm, the screen plate used in
the aforementioned discharge tube will advantageously be a screen with
overlapping crosslinked elongated holes according to FIG. 8.
Advantageously in accordance with the invention, C=5.50 mm and L=14.1 mm.
A sheet thickness of 2.2 mm is just as advantageous as a bridge width a
of 4.0 mm and a distance b of 5.0 mm. The open screen area F is in this
case 36.5%.

[0186]A Hi-Coater of the LH 100 type from Gebruder Lodige Maschinenbau
GmbH, Paderborn, Germany, which has a discharge tube for removing
adhering pairs as just described, will be referred to in this document as
a "removal Hi-Coater I".

[0187]The adhering pairs of coated catalyst rings removed in accordance
with the invention are generally not disposed of but rather reprocessed.
In other words, it will typically be attempted to recover the elements
present in the active composition thereof.

[0188]An inventive screen removal is generally performed under air
(especially in the case of all multielement oxide catalysts listed by way
of example in this document).

[0189]In the case of strongly hygroscopic or oxygen-sensitive coated
catalysts K or active compositions thereof, adhering pairs can also be
screened off with exclusion of moisture and/or oxygen (e.g. under
N2). Before the screen removal, the annular shaped coated catalyst
bodies K are generally supplied directly to a vessel which can be closed
air-tight, in which they can be stored. From this vessel (for example a
vat lined with a polypropylene shell), they can then be withdrawn, for
example for the purpose of a structured filling of reaction tubes,
following the teaching of DE-A 10 2004 023 249, and be introduced into
the reaction tube contemplated.

[0190]Alternatively to the coating process for preparing coated catalysts
K, coated catalysts K will frequently also be prepared by spraying the
annular shaped support bodies with a suspension of finely divided active
composition and/or finely divided precursor composition.

[0191]Advantageously in accordance with the invention, the procedure will
be as described in DE-A 4006935 and DE-A 10344844. The suspension, for
example aqueous suspension, of the finely divided active composition
and/or finely divided precursor composition which, in order to improve
the quality of the coating of the annular shaped support bodies,
generally comprises added organic binders (generally copolymers, for
example those based on vinyl acetate/vinyl laurate, or on vinyl
acetate/acrylate, or on styrene/acrylate, or on vinyl acetate/ethylene)
(for example in the form of an aqueous polymer dispersion) is sprayed at
elevated temperature onto the annular shaped support bodies until the
desired active composition content in the total catalyst weight has been
attained. Suitable apparatus for this purpose is especially fluidized bed
and moving bed apparatus. In this apparatus, the annular shaped support
bodies are fluidized in an ascending gas stream (for example hot air).
The apparatus usually consist of a conical or spherical vessel in which
the fluidizing gas is introduced from the bottom or from the top via a
central tube. The suspension is sprayed into the fluidized bed of the
annular shaped support bodies via nozzles from the top, laterally or from
the bottom. It is advantageous to use a guide tube arranged in the middle
or concentrically around the central tube. Within the central tube, there
is a higher gas velocity, which transports the annular shaped support
bodies upward. In the outer ring, the gas velocity is only slightly above
the fluidization velocity. Thus, the annular shaped catalyst supports are
moved in a vertical circular motion. Further details of this "spray
process" for preparing annular coated catalysts K can be found, for
example, in DE-A 10344844 and in DE-A 4006935. The latter also discloses
a moving bed apparatus which is particularly suitable in this regard.

[0192]Moreover, a production charge of coated catalysts K in the context
of this invention is a production amount of coated catalyst K which is
capable of covering the demand of at least two (better at least 10,
frequently at least 50, usually at least 100, in many cases at least 200
or at least 500) reaction tubes in the tube bundle reactor.

[0193]Annular coated catalysts K comprise, among other catalysts, those
coated catalysts whose active composition is a multielement oxide of the
general formula I

Mo12BiaFe.sub.bXc1Xd2Xe3Oy
(1)

where [0194]X1=Co and/or Ni, [0195]X2=Si and/or A1,
[0196]X3=Li, Na, K, Cs and/or Rb, [0197]0.2≦a≦1,
[0198]2≦b≦10, [0199]0.5≦c≦10,
[0200]0≦d≦10, [0201]0≦e≦0.5, and [0202]y=a
number which (with the prerequisite of charge neutrality) is determined
by the valency and frequency of the elements in I other than oxygen.

[0203]Such annular coated catalysts K can advantageously be prepared
according to the teaching of DE-A 100 49 873. To this end, an intimate
dry mixture is obtained from starting compounds of the elemental
constituents of the catalytically active oxide composition and is treated
thermally at from 150 to 350° C. to obtain a precursor
composition. In the coating process, using water as a binder, a layer of
the precursor composition is adhered to the annular shaped support bodies
and the coated annular shaped support bodies, which are dry to the touch,
are subsequently calcined at from 400 to 600° C.

[0204]These coated catalysts are suitable especially for the catalytic gas
phase partial oxidation of propylene to acrolein and of isobutene to
methacrolein. Advantageous partial oxidation conditions can likewise be
found in DE-A 10049873.

[0205]The process according to the invention is also relevant in the
preparation of annular coated catalysts K which have, as an active
coating, a multielement oxide which comprises the element V, Sb and at
least one element from Mo and W.

[0206]The preparation of such coated catalysts K is disclosed, for
example, by WO 2007/00922. Here too, a preferred preparation process is
the precursor composition coating process. However, it is equally
possible to employ the active composition coating process. Such coated
catalysts K are suitable especially for heterogeneously catalyzed partial
ammoxidations of organic starting compounds. Examples thereof are the
preparation of methylbenzonitriles and benzodinitriles from xylene.
Favorable partial ammoxidation conditions in this regard are likewise
disclosed by WO 2007/009922.

[0207]The process according to the invention is also of particular
significance when the catalysts are those annular coated catalysts K
whose catalytically active coating is a multielement oxide active
composition of the general formula II

[0222]They are suitable in particular for a heterogeneously catalyzed
partial gas phase oxidation of acrolein to acrylic acid. Advantageously,
the annular coated catalysts are obtainable here by the process of DE-A
10 2005 010645, of DE-A 10325488, of DE-A 10360058, of DE-A 10350822, of
DE-A 10 2004 025 445, of DE-A 10 2007 010 422, of US 2006/0205978 and of
EP-A 714 700, and the processes of the prior art cited in these
documents. A particularly preferred preparation process is the active
composition coating process according to EP-A 714 700. According to
German application 102007010422.9, it is possible to additionally add
finely divided molybdenum oxide to the active composition applied in
order to prolong the lifetime. The aforementioned documents additionally
disclose particularly favorable conditions for a heterogeneously
catalyzed partial gas phase oxidation of acrolein to acrylic acid.

[0223]The active composition coating thickness here will in particular be
from 10 to 1000 μm, preferably from 50 to 500 μm and more
preferably from 150 to 250 μm. Particularly favorable embodiments are
the exemplary embodiments of EP-A 714 700. A preferred ring geometry is
that where E×I×H=7 mm×4 mm×3 mm.

[0224]The process according to the invention is also of particular
relevance in the case of annular coated catalysts K whose active
composition is a multielement oxide which, has elements other than
oxygen, as well as the elements Mo and V, comprise at least one of the
two elements Te and Sb and at least one of the elements from the group
comprising Nb, Pb, Ta, W, Ti, Al, Zr, Cr, Mn, Ga, Fe Ru, Co, Rh, Ni, Pd,
Pt, La, Bi, B, Ce, Sn, Zn, Si, Na, Li, K, Mg, Ag, Au and In in
combination.

[0225]Their preparation is disclosed, for example, by WO 2004/108267. They
are suitable, inter alia, as catalysts for the heterogeneously catalyzed
partial gas phase oxidation of acrolein to acrylic acid, of propane to
acrolein and/or acrylic acid, of isobutane to methacrolein and/or
methacrylic acid and for the ammoxidation of propane to acrylonitrile and
of isobutane to methacrylonitrile (see also DE-A 10 2007 025 869).

[0226]However, the process according to the invention should also be
employed in the case of annular coated catalysts K whose active
composition comprises elemental silver on oxidic annular support bodies.
Such annular coated catalysts K are suitable especially for a
heterogeneously catalyzed partial gas phase oxidation of ethylene to
ethylene oxide (cf., for example, EP-A 496 470). Useful shaped support
bodies are in particular those which consist to an extent of at least 80%
by weight of aluminum oxide (e.g. Al2O3). As supported
catalysts for a heterogeneously catalyzed partial gas phase oxidation of
ethylene to ethylene oxide which comprise elemental silver in their
active composition applied to an oxidic annular shaped support body, the
annular supported catalyst of EP-A 619 142, EP-A 624 398, EP-A 804 289
and EP-A 937 498 should also be emphasized. For all of these annular
coated catalysts K, the process according to the invention is a suitable
option.

[0228]The process according to the invention also has increased relevance
in the case of annular coated catalysts K whose active composition is at
least one multielement oxide which comprises oxidic TiO2 units to an
extent of at least 60% by weight but to an extent of not more than 99% by
weight, and oxidic V2O5 units to an extent of at least 1% by
weight but to an extent of not more than 40% by weight. Frequently, the
aforementioned multielement oxide active compositions also comprise up to
1% by weight of Cs, up to 1% by weight of P and up to 10% by weight of
oxidic Sb2O3 units. In addition, they may comprise further
promoters which promote the activity and selectivity of the coated
catalyst K.

[0231]The process according to the invention is also outstandingly
suitable for the annular multielement oxide coated catalysts which
comprise Mo and Fe, are disclosed in DE-A 10 2005 055 827 and are
suitable especially for the oxidation of methanol to formaldehyde.

[0232]Otherwise, the fixed catalyst bed charging of the reaction tubes of
the tube bundle reactor is as described in German application
102007017080.9.

[0233]I. Charging of a Thermal Tube with a Fixed Catalyst Bed Comprising
Annular Coated Catalysts, a Removal of Adhering Pairs Having been
Performed Before the Introduction of the Annular Coated Catalysts

[0234]The thermal tube (V2A steel; external diameter 33.7 mm, wall
thickness 2 mm, internal diameter 29.7 mm, length: 350 cm, and a
thermowell centered in the middle of the thermal tube (external diameter
10 mm) for accommodating a stationary multithermoelement with which the
temperature in the thermal tube can be determined over its entire length)
was charged from the top downward as follows:

[0236][0237]length 90 cm [0238]fixed catalyst bed charge with a
homogeneous mixture of 30% by weight of steatite rings ST, 30% by weight
of annular coated catalysts K1 according to working example 2 of WO
2004/108267, but with preceding removal of adhering pairs (7.1
mm×4.0 mm×3.2 mm; Mo12V3W1.2Cu2.4Ox;
the annular shaped support bodies are coated and the adhering pairs are
removed with a Hi-Coater I) and 40% by weight of spherical coated
catalysts KU1 (prepared like the annular coated catalysts K1, but with
spherical shaped support bodies of steatite having a diameter of 4-5 mm,
and using water as a binder and a proportion by weight of 20% by weight
of the active composition coating;

[0245]From the top downward, the first 175 cm were thermostatted by means
of a salt bath A pumped in countercurrent, which was supplied with the
temperature THA. The second 175 cm were thermostatted by means
of a salt bath B pumped in countercurrent, which was supplied with the
temperature THB. Both salt baths were a mixture of 53% by
weight of potassium nitrate, 40% by weight of sodium nitrite and 7% by
weight of sodium nitrate.

[0246]The above-described thermal tube was charged continuously with a
reaction gas input mixture of the following contents: [0247]4.8% by
volume of acrolein, [0248]0.5% by volume of acrylic acid, [0249]0.2% by
volume of propylene, [0250]5.5% by volume of molecular oxygen, [0251]0.5%
by volume of CO, [0252]1.1% by volume of CO2, [0253]5.7% by volume
of water, and [0254]81.5% by volume of nitrogen.

[0255]The reaction gas mixture flowed through the thermal tube from the
top downward. The pressure at the inlet to the thermal tube was 2.0 bar
(absolute). The loading of the fixed catalyst bed with acrolein was 140 l
(STP)/lh.

[0256]THA was adjusted to 275° C. and THB to
279° C. The reaction gas input mixture was preheated to
220° C.

[0257]At a conversion of the acrolein of approx. 99.5 mol % and a
selectivity of acrylic acid formation of 95.0 mol % based on single pass
of the reaction gas mixture through the thermal tube, the hotspot
temperature in the thermal tube was 323° C. The position of the
hotspot maximum was, in flow direction of the reaction gas, 45 cm after
the start of section 2.

II. Repetition of the Partial Oxidation from A) I, but with Controlled
Doping of the Fixed Catalyst Bed Introduced into the Thermal Tube with a
Tandem Adhering Pair Obtained in the Course of Removal of Adhering Pairs
in the Preparation of the Annular Coated Catalysts K1 (the Total Amount
of Adhering Pairs Removed was 0.24% by Weight)

[0258]The fixed catalyst bed was charged as in A) I. In flow direction of
the reaction gas, 45 cm after the start of section 2, however, a tandem
adhering pair (0.02% by weight based on the total weight of annular
coated catalysts K1 introduced) was positioned deliberately between the
inner wall of the thermal tube and the outer wall of the thermowell such
that its longitudinal axis pointed in the flow direction of the reaction
gas. Otherwise, the procedure was as in A) I and the thermal tube charge
was also conducted to the end in the same way.

[0259]With an unchanged position of the hotspot temperature, it was
increased to 325° C.

III. Repetition of the Partial Oxidation from A) I, but with Controlled
Doping of the Fixed Catalyst Bed Introduced into the Thermal Tube with a
Fused Adhering Pair Obtained in the Course of Removal of Adhering Pairs
in the Preparation of the Annular Coated Catalysts K1

[0260]The fixed catalyst bed was charged as in A) I. As the first 70 cm of
reaction tube length viewed in flow direction of the reaction gas were
still uncharged and the remaining reaction tube length had already been
charged, a fused adhering pair was wedged (jammed) between the inner wall
of the thermal tube and the outer wall of the thermowell 40 cm after the
start of section 2 in flow direction. Otherwise, the procedure was as in
A) I and the thermal tube filling, after the adhering pair had been
wedged in, was also conducted to the end in the same way.

[0261]The position of the hotspot maximum was now as early as (in flow
direction of the reaction gas) 40 cm after the start of section 2. It was
now 324° C.

B) Heterogeneously Catalyzed Partial Gas Phase Oxidation of Acrolein to
Acrylic Acid in a Working Tube (which is Represented by the Thermal Tube
in A) I)

[0262]A working tube (V2A steel; external diameter 30 mm; wall thickness 2
mm, internal diameter 26 mm, length 350 cm) was charged as described
above with a fixed catalyst bed comprising annular coated catalysts K1
(with preceding removal of adhering pairs). To determine the profile of
the reaction temperature in the working tube, it comprised, introduced
directly into the center, a multithermoelement (external diameter=4 mm;
in the industrial scale tube bundle reactor, this procedure is not
possible; an industrial scale working tube (which does not comprise a
thermoelement) would therefore comprise a somewhat larger total amount of
active composition overall and therefore require THA,
THB lower by 1° C. for the same acrolein conversion).

I Ideal Charge (without Adhering Pairs) of the Working Tube with the Fixed
Catalyst Bed (from the Top Downward)

[0271]In this working tube, under the same conditions as in the thermal
tube under A) I, a heterogeneously catalyzed partial gas phase oxidation
of acrolein to acrylic acid was performed (for the reasons addressed
above, THA=276° C. and THB=280° C. in
order to achieve the same acrolein conversion of 99.5 mol %).

[0272]The hotspot temperature was 323° C. as in the thermal tube.
The position of the hotspot maximum was, as in A) I, 45 cm after the
start of section 2 in flow direction of the reaction gas.

II. In the same way as the Thermal Tube in A) II, the Fixed Catalyst Bed
Charge of the Working Tube was Doped with a Tandem Adhering Pair.

[0273]As a result, a hotspot temperature of 325° C., increased by
2° C., was established with the same position of the hotspot
maximum.

III. The Fixed Catalyst Bed Charge was Undertaken as in B) I, Except that,
in the Portion of Annular Coated Catalysts 1 Forming Section 4, before it
was Emptied into the Working Tube, a Tandem Adhering pair was Randomly
Added (after the Addition, the Portion was Shaken).

[0274]The resulting partial oxidation results were indistinguishable from
those in B) I under otherwise identical operating conditions.

C) Heterogeneously Catalyzed Partial Gas Phase Oxidation of o-xylene to
Phthalic Anhydride in a Thermal TubeI. Charging of a Thermal Tube with a
Fixed Catalyst Bed Comprising Annular Coated Catalysts, a Removal of
Adhering Pairs Having been Performed Before the Introduction of the
Annular Coated Catalysts.

[0275]The thermal tube (V2A steel; internal diameter: 25 mm, wall
thickness: 2 mm; length: 385 cm; a thermowell centered in the middle of
the reaction tube (external diameter 4 mm) for accommodating a single
thermoelement movable along the reaction tube in order to determine the
reaction temperature along the reaction tube) was charged from the top
downward as follows:

[0277][0278]length 170 cm [0279]annular coated catalyst according to
example 7 of DE-A10344844, but with removal of adhering pairs (suspension
spray process; support geometry=8 mm×5 mm×6 mm
(E×I×H); removal of adhering pairs by means of a Mogensen
Sizer I; the multimetal oxide active composition coating comprised 0.08%
by weight of P; 5.75% by weight of V2O5 units; 1.6% by weight
of Sb2O3 units; 0.4% by weight of Cs and 92.17% by weight of
TiO2 units);

Section 3:

[0279][0280]length 130 [0281]annular coated catalyst according to
example 4 of DE-A10344844, but with removal of adhering pairs (suspension
spray process; support geometry=8 mm×5 mm×6 mm
(E×I×H); removal of adhering pairs by means of a Mogensen
Sizer I; the multimetal oxide active composition coating comprised 0.15%
by weight of P; 7.5% by weight of V2O5 units; 3.2% by weight of
Sb2O3 units; 0.1% by weight of Cs and 89.05% by weight of
TiO2 units).

[0282]The thermal tube was flowed around by a salt bath (a mixture of 53%
by weight of potassium nitrate, 40% by weight of sodium nitrite and 7% by
weight of sodium nitrate) which had a temperature of 350° C.

[0283]The above-described thermal tube was charged with a reaction gas
input mixture composed of 2% by volume of o-xylene and 98% by volume of
air. The charge gas flow rate was 4 m3 (STP)/h at an inlet pressure
of 1.4 bar (absolute). The reaction gas mixture flowed through the
thermal tube from the top downward. At a conversion of the o-xylene,
based on single pass of the reaction gas mixture through the thermal
tube, of 99.97 mol %, the selectivity of phthalic anhydride formation was
81.7 mol %. The hotspot temperature in the reaction tube was 452°
C. The position of the hot spot maximum in flow direction of the reaction
gas was 90 cm beyond the start of section 2.

II. Repetition of the Partial Oxidation from C) I, but with Controlled
Doping of the Fixed Catalyst Bed Introduced into the Thermal Tube with a
Tandem Adhering Pair Obtained in the Course of Removal of Adhering Pairs
in the Preparation of the Annular Coated Catalysts from Section 2 (the
Total Amount of the Adhering Pairs Removed was 0.3% by Weight)

[0284]The fixed catalyst bed was charged as in C) I. In flow direction of
the reaction gas, 90 cm beyond the start of section 2, however, a section
2 tandem adhering pair (0.092% by weight based on the total weight of
coated catalysts introduced over all into the thermal tube) was
positioned between the inner wall of the thermal tube and the outer wall
of the thermowell such that its longitudinal axis pointed in the flow
direction of the reaction gas. Otherwise, the procedure was as in C) I
and the thermal tube charge was also conducted to the end in the same
way.

[0285]With an unchanged position of the hotspot temperature, it increased
to 463° C.

[0286]U.S. Provisional Patent Application No. 60/944,327, filed Jun. 15,
2007, is incorporated into the present patent application by literature
reference. With regard to the above-mentioned teachings, numerous changes
and deviations from the present invention are possible. It can therefore
be assumed that the invention, within the scope of the appended claims,
can be performed differently from the way described specifically herein.